The success of clozapine in treating schizophrenia has spurred the search for new compounds with similar behavioral effects. The present experiments were conducted to compare the behavioral effects of clozapine with those of the conventional antipsychotic haloperidol and the candidate antipsychotics olanzapine and seroquel in squirrel monkeys. The effects of each drug were determined in observational studies and avoidance-related procedures typically used to evaluate antipsychotics. Drugs also were studied in clozapine-discrimination procedures. Results indicate that 1)all drugs had effects in avoidance-related procedures indicative of antipsychotic efficacy; 2) haloperidol and olanzapine but not clozapine and seroquel produced observable effects that previously have been correlated with side-effects produced by conventional antipsychotics; and 3) seroquel but not haloperidol or olanzapine fully reproduced the discriminative-stimulus effects of clozapine. These findings indicate that the behavioral effects of clozapine may overlap more completely with those of seroquel than with those of olanzapine or haloperidol.